FIG. 1 shows a radio or wireless communications system 1 where wireless terminals 2 (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks (shown as a cloud 3). In a cellular communications system, the radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of a radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a controller node (such as a radio network controller (RNC) or a base station controller (BSC)) which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. Specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3GPP). The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE). Long Term Evolution (LTE) is a variant of a 3GPP radio access technology where the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller is (RNC) node are distributed between the radio base stations nodes (eNodeB's in LTE). As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
In radio access networks like UTRAN and E-UTRAN, it may be desirable to minimize human-based “drive testing” that operators need to perform to troubleshoot and optimize their networks. One alternative for minimizing drive test (MDT) is for UEs to perform measurements and report them to the radio network which may then be forwarded if desired or needed. Example UE reporting methods for these measurements include Logged Reporting and Immediate Reporting. For LTE, a UE can either be in a radio resource control (RRC)-Connected mode (the UE is involved in an active communication) or an RRC-Idle mode (the UE is not involved in an active communication but is “camped” on a cell). In certain LTE networks, Immediate Reporting may be used in RRC-Connected mode and Logged Reporting may be used in RRC-Idle mode. For immediate reporting, the MDT measurements by UEs in RRC-Connected mode are reported to the network (e.g., eNB/RNC) at the time of reporting. For logged reporting, the MDT measurements by UEs in RRC-Idle mode are stored in a measurement log and reported to the network at later points in time when configured conditions are satisfied. Measurement logs may include multiple events and measurements taken over time.
Although immediate reporting is used for connected mode, there are situations that cannot be handled by immediate reporting including when the UE cannot communicate with the RAN, e.g., the UE's radio link fails. In this situation, the UE typically discards the MDT measurements. But from an operator's perspective, it would still be desirable to receive the MDT measurements at a later time if possible because that MDT measurement information may still be valuable for managing the network.